Examples

Example 1: Industrial melanism in the peppered moth

Wallace (1858) hypothesized that insects that resemble in color the trunks on which they reside will survive the longest, due to the concealment from predators. The relatively rapid rise and fall in the frequency of mutation-based melanism in populations (Figure 8.1) that occurred in parallel on two continents (Europe, North America), is a compelling example for rapid microevolution in nature caused by mutation and natural selection. The hypothesis that birds were selectively eating conspicuous insects in habitats modified by industrial fallout is consistent with the data (Majerus, 1998; Cook, 2000; Coyne, 2002; Grant, 2002).

Example 2: Warning coloration and mimicry

In his famous book, Wallace (1889) devoted a comprehensive chapter to the topic "warning coloration and mimicry with special reference to the Lepidoptera". One of the most conspicuous day-flying moths in the Eastern tropics was the widely distributed species Opthalmis lincea (Agaristidae). These brightly colored moths have developed chemical repellents that make them distasteful, saving them from predation (Miillerian mimetics). O. lincea (Figure 8.2A) is mimicked by the moth Artaxa simulans (Liparidae), which was collected during the voyage of the Challanger and later described as a new species (Figure 8.2B). This survival mechanism is called Batesian mimetics (Kettlewell, 1965).

form: typica form: carbonaria species: Biston betularia

form: typica form: carbonaria species: Biston betularia

Figure 8.1 Industrial melanism in populations of the peppered moth (Biston betularia). Previously to 1850, white moths peppered with black spots (typica) were dominant in England (A). Between 1850 and 1920, as a response to air pollution that accompanied the rise of heavy industry, typica was largely replaced by a black form (carbonaria) (B), produced by a single allele, since dark moths are protected from predation by birds. Between 1950 and 1995, this trend reversed, making form (B) rare and (A) again common. (Adapted from Kettlewell, 1965).

Ophtalmis lincea Artaxa Simulans

Figure 8.2 Insects have evolved highly efficient survival mechanisms that were described in detail by A.R. Wallace. One common moth species (Opthalmis lincea) (A) contains chemical repellents to make the insects distasteful. This moth is mimicked by a second species (Artaxa simulans) (B) From Wallace (1889).

Example 3: Darwin s finches

Darwin's finches exemplify the way one species' gene pools have adapted for long-term survival via their offspring. The Darwin's finches diagram below illustrates the way the finch has adapted to take advantage of feeding in different ecological niches (Figure 8.3).

Their beaks have evolved over time to be best suited to their feeding situation. For example, the finches that eat grubs have a thin extended beak to poke into holes in the ground and extract the grubs. Finches that eat buds and fruit would be less successful at doing this, while their claw like beaks can grind down their food and thus give them a selective advantage in circumstances where buds are the only real food source for finches.

Example 4: The role of size in horses' lineage

Maybe the horses' lineage offers one of the best-known illustrations regarding the role of size, profoundly documented through a very well-known fossil record. In the early Eocene (50-55million years ago), the smallest species of horses' ancestors had approximately the size of a cat, while other species weighted up to 35 kg. The Oligocene species, approximately

Beaks adaptive radiation

Original Finch

Large Ground

Finch

Large Ground

Small Ground

— Medium Ground

Sharp Beaked Ground Medium Tree

Woodpecker —

Vegetarian —

Large Tree

Beaks adaptive radiation

Large Ground

Finch

Sharp Beaked Ground Medium Tree

Woodpecker —

Vegetarian —

Warbler Finch

Figure 8.3 Darwin's finches diagram.

Warbler Finch

Figure 8.3 Darwin's finches diagram.

30 million years ago, were bigger, probably weighing up to approximately 50 kg. In the middle Miocene, approximately 17-18 million years ago, grazing "horses" of the size up to 100 kg were normal. Numerous fossils have shown that the weight reached approximately 200 kg 5 million years ago and approximately 500kg 20,000 years ago. Why did this increase in size offer a selective advantage?

Figure 8.4 shows a model in form of a STELLA diagram that has been used to answer this question. The model equations are shown in Table 8.1.

The model has been used to calculate the efficiency for different maximum weights. Heat loss is proportional to weight to the exponent 0.75 (Peters, 1983). The growth rate follows also the surface, but the growth rate is proportional to the weight to the exponent 0.67 (see equations in Table 8.1). The results are shown in Table 8.2 and the conclusion is clear: the bigger the maximum weight, the better the eco-exergy efficiency. This is of course not surprising because a bigger weight means that the specific surface that determines the heat loss by respiration decreases. As the respiration loss is the direct loss of free energy, relatively more heat is lost when the body weight is smaller. Notice that the maximum size is smaller than the supper maximum size that is a parameter to be used in the model equations (see also Table 8.2).

The evolutionary theory at the light of ecosystem principles

Although living systems constitute very complex systems, they obviously comply with physical laws (although they are not entirely determined by them), and therefore in ecological theory it should be checked that each theoretical explanation conforms to basic laws of physics. First, one needs to understand the implications of the three generally accepted laws of thermodynamics in terms of understanding organisms' behavior and ecosystems' function. Nevertheless, although the three laws of thermodynamics are effective in describing system's behavior close to the thermodynamic equilibrium, in far from equilibrium systems, such as ecosystems, it has been recognized that although the org org

Figure 8.4 The growth and respiration follow allometric principles (Peters, 1983). The growth equation describes logistic growth with a maximum weight. The food efficiency is found as a result of the entire life span, using the ^-values for mammals and grass (mostly Gramineae). The equations are shown in Table 8.1.

Figure 8.4 The growth and respiration follow allometric principles (Peters, 1983). The growth equation describes logistic growth with a maximum weight. The food efficiency is found as a result of the entire life span, using the ^-values for mammals and grass (mostly Gramineae). The equations are shown in Table 8.1.

Table 8.1 Model equations d(org(t))/dt = (growth-respiration) INIT org = 1kg

INFLOWS: growth = 3 X org(0 67) X (1-org/upper maximum size) OUTFLOWS: respiration = 0.5 X org(3/4) d(total_food(t))/dt = (consumption) INIT total_food = 0

INFLOWS: consumption = growth + respiration food_eff % = 2127 X 100 X org(t)/(200 X total_food(t))

Note: See the conceptual diagram Figure 8.4.

three basic laws remain valid, they represent an incomplete picture when describing ecosystem functioning. This is the purpose of "irreversible thermodynamics" or "non-equilibrium thermodynamics". A tentative Ecological Law of Thermodynamics was proposed by Jorgensen (1997) as: If a system has a through-flow of Exergy, it will attempt to utilize the flow to increase its Exergy, moving further away from thermodynamic

Table 8.2 Eco-exergy efficiency for the life span for different maximum sizesa

Maximum size (kg)

Eco-exergy efficiency (percent)

Upper maximum size parameter (kg)

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